NeoCal Documentation

NeoCal for Palm OS User Guide

Comparison of Input Methods

This calculator was designed to work equally well using either the Simple, Precedence, or RPN input methods. The simple input method is most familiar and allows entering calculations like to get the desired result of 5. A more complex example is 2 + 3 x 5 = 17, which can be entered two ways, or . The first sequence required the use of parentheses to instruct the calculator to multiply before adding the numbers (since the Simple input method does not conform to this algebraic convention). The second sequence avoided the use of parentheses by re-ordering the operations to generate the correct result of 17.

The Precedence input method is an improvement over the simple input method in that binary operations are automatically performed before multiplication and division operations which are performed before addition and subtraction operations, reducing the need for parentheses. For example, the previous calculation can be entered without the parentheses as to obtain the result of 17. Additionally, yields 18 since the power function is performed before the multiplication.

The benefits of the RPN, or Reverse Polish Notation, input method over the simple and precedence input methods become apparent when calculating complex expressions. Fewer mistakes are made since fewer keystrokes are required and the intermediate results are always displayed (providing feedback during the calculation, not just at the end). The order of the calculation is changed to avoid using parentheses, as in the previous example, so that the expression is evaluated from the inside working outward.

The general rule of thumb for RPN calculators is to enter the values, then the operation. Thus, becomes . The key is used to separate numbers when entering more than one in succession. In the example, 2 + 3 x 5 = 17, the RPN method could be evaluated using either , or . Looking at these two sequences, we can isolate which always shows the result of 15. The two sequences then become 15 and 15 which are more easily recognizable as 17.

Keystroke savings are realized in calculations that cannot be reordered to a form without parentheses. Let's look at the example 2 x 4 + 3 x 5 = 23. Using the simple input method we could calculate this expression as , or without using parentheses, . Using RPN, the sequence becomes . Saving one keystroke is not that significant, but this is still a relatively simple calculation. One important distinction between the two input methods is demonstrated by the sub expression 2 x 4. Using the simple input method, this sometimes needs to be enclosed in parentheses (when not located at the beginning of the expression) and sometimes not. Using RPN, this sub expression is always entered the same way. This consistency also contributes to fewer mistakes being made.

One final point is that most of the calculations require the operand to be entered before the operation is executed. For example, calculating the square root of 2 is always entered and the inverse of 10 is entered regardless of the current input method. The RPN input method just extends this methodology to all of the calculator's functions.

The input method can be chosen in the Preferences dialog. If you'd like to learn more about how an RPN calculator works, check out the RPN Tutorial chapter of this guide. With all of the input methods, all of the calculator functions are available allowing you to work the way you're most comfortable.

The input method can be temporarily changed using the , , or buttons. The clear operation restores the input method to the setting specified in the Preferences dialog.